1. Field of the Invention
This invention relates to the field of surgery and more particularly to prosthetic grafts for vascular and non-vascular applications.
2. Description of the Related Art
U.S. Pat. No. 4,319,363 discloses a prosthesis for revascularisation made from a biomaterial and it describes a method for making the prosthesis in which a mesh covered silicon rod (mandril) is inserted into a living host animal, preferably a sheep, collagenous tissue is allowed to grow around the mandril for about twelve to fourteen weeks after which the implant is removed and subjected to glutaraldehyde tanning to form a prosthesis for revascularisation.
The current invention is based on the surprising discovery that certain variations in the structure, geometry and quantity of the synthetic material or substrate on which it is supported promote improved tissue growth and/or allow the creation of new biological composite materials (xe2x80x9cbiomaterialsxe2x80x9d) suitable for both vascular and non-vascular surgical application.
In accordance with a first broad aspect of the invention there is provided a biomaterial suitable for use in surgery in a human patient, comprising:
a coherent layer of non-human collagenous tissue which has been subjected to glutaraldehyde tanning so as to comprise cross-linked collagen fibrils, and
a reinforcement of synthetic material embedded within the coherent layer, said synthetic material having structure features for promoting said embedding, said synthetic material having an average in situ more than 50 of said features per square centimeter.
Preferably, the synthetic material has more than 100 of said features per square centimeter.
Preferably also, the synthetic material is a fibre mesh and the features for promoting said embedding are the reticulations of the mesh. The fibre mesh may be constructed from polyester yarn. The polyester yarn may also be augmented with polyurethane, either in the form of strands of polyester dipped in polyurethane or strands of polyurethane wound around strands of polyester.
Alternatively, the synthetic material may be particulate in nature, in which case said features may be constituted by individual particles of that material.
Preferably further, the biomaterial is in the shape of a tube. Alternatively, the biomaterial is in the form of a sheet.
Preferably also, the biomaterial is smooth on one side to inhibit attachment to surfaces in the patient proximate said one side and rough on the other side to encourage said attachment.
In the case where the synthetic material is a mesh, the mesh may be embedded in the coherent layer such that the mesh structure is in a loose unstretched state.
In accordance with a second broad aspect of the invention there is provided a method of producing a biomaterial, comprising the steps of:
positioning a tubular synthetic fibre mesh structure about a support rod or tube;
implanting the mesh covered support rod or tube in the body of a living, non-human, host animal at such location as to cause growth of collagenous tissue thereon;
allowing said collagenous tissue to grow on the implant until there is formed a coherent wall of said tissue encompassing the rod or tube and having the mesh structure embedded therein;
removing the implant and said coherent wall of collagenous tissue from the body of the host animal;
subjecting said coherent wall of collagenous tissue to glutaraldehyde tanning in order to produce cross-linking of collagen fibrils therein so as to increase the strength of the wall and also to impart immunological inertness and sterility thereto; and
removing the rod or tube from within the coherent wall of collagenous tissue at any time subsequent to removal of the rod or tube and coherent wall of collagenous tissue from the body of the host animal;
wherein the tubular synthetic fibre mesh structure fits over the support rod in a loose unstretched state.
Optionally, the tubular mesh may be substantially larger in a longitudinal direction than the support rod or tube.
The tubular biomaterial thereby produced may if desired be cut length-wise to produce a sheet.
In accordance with a third broad aspect of the invention there is provided a method of producing a biomaterial, comprising the steps of:
implanting a support sheet in the body of a living, non-human, host animal at such a location as to cause growth of collagenous tissue thereon;
allowing said collagenous tissue to grow on the implant until there is formed a coherent layer of said tissue on both sides of the support sheet;
removing the implant and said coherent layer of collagenous tissue from the body of the host animal;
subjecting said coherent layer of collagenous tissue to glutaraldehyde tanning in order to produce cross-linking of collagen fibrils therein so as to increase the strength of the layer and also to impart immunological inertness and sterility thereto; and
separating the support sheet from the coherent layer of collagenous tissue at any time subsequent to removal of the implant from the body of the host animal to form a pocket, pouch or envelope of collagenous material.
Preferably, a synthetic material having structure features for promoting embedding of the synthetic material within the collagenous tissue is positioned on the support sheet so as to encompass both sides of the support sheet.
Preferably also, the synthetic material is a mesh structure. The synthetic material may have the features required for the first broad aspect of the current invention. The positioning of the synthetic material may be in accordance with the second broad aspect of the invention.
Preferably, for all first, second and third aspects of the invention, the host animal is a sheep. Preferably too, the implant is made beneath the cutaneous muscle of the lateral thoracic wall of the host animal. Preferably further, the implant is allowed in the host animal for at least ten weeks. Preferably also, the tanning step is carried out by immersing the implant and wall of tissue in a bath of buffered glutaraldehyde after removal from the body of the host animal and before removal of the support or tube. Preferably further, the biomaterial is rehydrated for use using heparin.